Gangliosides are glycosphingolipids that are present in high numbers on cells of neural crest origin as well as on a wide variety of tumor cells of neuroectodermal origin. Portoukalian et al., Eur. J. Biochem. 94:19-23 (1979); Yates et al., J. Lipid Res. 20:428-436 (1979). More specifically, expression of the gangliosides GD2, GD3, and GM2 has been reported in neuroblastoma, lung small cell carcinoma, and melanoma, each of which are highly malignant neuroectodermal tumors. J. Exp. Med., 155:1133 (1982); J. Biol. Chem. 257:12752 (1982); Cancer Res. 47:225 (1987); Cancer Res. 47:1098 (1987); Cancer Res. 45:2642 (1985); Proc. Natl. Acad. Sci. U.S.A. 80:5392 (1983).
The chemical structure of gangliosides includes a hydrophilic carbohydrate portion (one or more sialic acids linked to an oligosaccharide) attached to a hydrophobic lipid moiety composed of a long-chain base (sphingosine) and a fatty acid (ceramide). (G is an abbreviation for ganglioside and M, D, and T are abbreviations for mono, di, and tri, respectively; for further discussion of ganglioside nomenclature, see, Lehninger, Biochemistry, pp. 294-296 (Worth Publishers, 1981) and Wiegandt, in Glycolipids: New Comprehensive Biochemistry (Neuberger et al., ed., Elsevier, 1985), pp. 199-260; see, also, FIG. 1 for a schematic of ganglioside biosynthesis).
Gangliosides are believed to be involved in cell recognition, immunosuppression, adhesion and signal transduction. The ceramide portion anchors the ganglioside into the cell membrane and may, thereby, modulate intracellular signal transduction as a second messenger. The ganglioside designated GM2 is one of a group of sialic acid residue-containing glycolipids and is uniquely characterized by its presence in only trace amounts in normal cells and its upregulation in a variety of cancer cells such as, for example, lung small cell carcinoma, melanoma, and neuroblastoma.
Because they are immunogenic, gangliosides have received much attention as possible vaccine targets. For example, vaccination with a GM2 ganglioside, has been shown to stimulate high levels of anti-GM2 antibodies in melanoma patients. GM2 vaccines comprising either bacilli Calmette-Guerin (BCG) or, more recently, keyhole limpet hemagglutinin (KLH) as adjuvant have been tested in human clinical trials. Livingston et al., Proc. Natl. Acad. Sci U.S.A. 84:2911-2915 (1987); Livingston, In “Immunity to Cancer II.” Eds MS Mitchell, Pub Alan L. Liss, Inc., NY; Irie et al. U.S. Pat. No. 4,557,931; Kirkwood et al. J. Clin. Oncol. 19(5):1430-1436 (2001); Chapman et al. Clin. Cancer Res. 6(3):874-879 (2000).
In an effort to develop a therapeutic agent against GM2-positive cells, a number of investigators have reported the production of anti-GM2 antibodies. For example, Yamaguchi et al., described the isolation of lymphocytes from a GM2-vaccinated patient and the transformation of those lymphocytes with Epstein-Barr virus to produce an antibody (designated 3-207) simultaneously reactive for both GM2 and GD2. Proc. Natl. Acad. Sci. USA 87:3333-3337 (1990). Similarly, Irie et al., disclosed a human monoclonal anti-GM2 antibody for melanoma treatment. Lancet 1:786-787 (1989); see, also, Tai et al., Proc. Nat. Acad. Sci. U.S.A. 80:5392-5396 (1983) (disclosing a human anti-GM2 monoclonal antibody designated L55) and Yamasaki et al. U.S. Pat. No. 4,965,498 (disclosing a monoclonal antibody specific to a sugar chain containing an N-glycolylneuramine acid and having the ability to bind to at least N-glycolyl GM2 ganglioside). Furthermore, Ritter et al., disclosed antibodies produced following immunization with a lipopolysaccharide antigen of Campylobacter jejuni that reportedly binds to monosialogangliosides, including both GM2 and GM1. Int. J. Cancer 66(2):184-190 (1996).
Nakamura et al. have described two murine anti-GM2 monoclonal IgM antibodies, KM696 and KM697, as well as corresponding chimeric antibodies, KM966 and KM967, constructed by replacing the variable domain heavy and light chain cDNAs of a human IgG1 with the corresponding variable domain heavy and light chain cDNAs of KM696 and KM697, respectively. Cancer Research 54:1511-1516 (1994); U.S. Pat. Nos. 5,830,470 and 5,874,255. These investigators also reported CDR-grafted variants of the KM696/KM966 and the KM697/KM967 antibodies designated KM8966 and KM8967, respectively. U.S. Pat. Nos. 5,939,532 and 6,042,828. Indirect immunofluorescence staining of tumor cell lines with the KM966 chimeric antibody demonstrated that GM2 was expressed on pulmonary tumor cells and leukemia cells as well as neuroectodermal origin tumor cells.